[PATCH 1/2] hyper-v: Mark inner union in hv_kvp_exchg_msg_value as packed
From: Thomas Weißschuh
Date: Thu Jan 15 2026 - 02:36:00 EST
The unpacked union within a packed struct generates alignment warnings
on clang for 32-bit ARM:
./usr/include/linux/hyperv.h:361:2: error: field within 'struct hv_kvp_exchg_msg_value'
is less aligned than 'union hv_kvp_exchg_msg_value::(anonymous at ./usr/include/linux/hyperv.h:361:2)'
and is usually due to 'struct hv_kvp_exchg_msg_value' being packed,
which can lead to unaligned accesses [-Werror,-Wunaligned-access]
361 | union {
| ^
With the recent changes to compile-test the UAPI headers in more cases,
this warning in combination with CONFIG_WERROR breaks the build.
Fix the warning.
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202512140314.DzDxpIVn-lkp@xxxxxxxxx/
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Closes: https://lore.kernel.org/linux-kbuild/20260110-uapi-test-disable-headers-arm-clang-unaligned-access-v1-1-b7b0fa541daa@xxxxxxxxxx/
Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Link: https://lore.kernel.org/linux-kbuild/29b2e736-d462-45b7-a0a9-85f8d8a3de56@xxxxxxxxxxxxxxxx/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
---
include/uapi/linux/hyperv.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/uapi/linux/hyperv.h b/include/uapi/linux/hyperv.h
index aaa502a7bff4..1749b35ab2c2 100644
--- a/include/uapi/linux/hyperv.h
+++ b/include/uapi/linux/hyperv.h
@@ -362,7 +362,7 @@ struct hv_kvp_exchg_msg_value {
__u8 value[HV_KVP_EXCHANGE_MAX_VALUE_SIZE];
__u32 value_u32;
__u64 value_u64;
- };
+ } __attribute__((packed));
} __attribute__((packed));
struct hv_kvp_msg_enumerate {
--
2.52.0